The present invention relates to foundry work and particularly to the art of producing foundry moulds and cores by using self-hardening plastic or liquid moulding sand mixtures.
Most efficiently the present invention may be used in manufacturing heavy foundry moulds and cores.
The use of such moulds and cores, produced by the known procedure, presents a problem arising from the fact that both the moulds and cores are susceptible to deformation at high temperatures. This is displayed, for example, in using a mixture of refractory pulverized material, such as highsilica sand, olivine or zircon, which act as a filler, and is hereinafter referred to as a moulding sand, sodium silicate as a binder and bicalcium silicate or materials containing the foregoing compound. In addition, the sand is tempered with water and a foaming agent may also be used (see, for example, French Pat. No. 1,342,529, British Pat. No. 1,085,651, and German Provisional Specification No. 1,249,461). The method involves a number of operations associated with the shaping of foundry moulds and cores from the sand obtained and with their weathering to be hardened. Hardening time is rather long ranging from 40 to 50 min. Compressive strength of the moulds and cores produced does not exceed 1.5-2.0 kg/cm.sup.2.